The present invention relates to a bar code printer by which a photosensitive product is provided with latent images of bar codes during the manufacture of the photosensitive product.
In the manufacture of photosensitive products such as photographic films or the like (which are hereinafter referred to simply as film), it is typical to provide a film with latent images of bar codes indicating necessary information, such as frame numbers, as well as the frame numbers which are later photographically developed during the processing of the exposed film. The bar codes are automatically read by an optical reader or other bar code readers to provide information pertaining to the film. In particular, when printing extra prints from the film, the bar code is automatically read to position in the printing position that frame of the film whose extra print is desired. The bar code is also printed on a print made from the film, and used to identify the frame number of the film from which the print was made. If the bar code reader makes an error in reading the bar code of a customer's film, the printer will necessarily make a print other than that requested by the customer. Accordingly, strict quality control should be maintained in printing bar codes on films.
To indicate frame numbers by bar codes printed on a film, a DX bar code system has heretofore been used to indicate a manufacturer or the like, and a bar code indicating a frame number appears after a DX code on the film. However, because a wide space must be provided between the frame number bar code and the DX code, it often happens that the frame number bar code is disposed between adjacent frames, and are thus interrupted when the film is cut into several strips. And because the frames as actually exposed are not always accurately located adjacent frame number bar codes, the wider the space occupied by each frame number bar code, the greater the chances of cutting the film in a manner to interrupt the frame number bar codes.
In the DX bar code system, the film is formed with notches in one margin thereof, one for each exposed frame. During processing, the notch is used to provide a timing signal in order to locate each frame in a proper exposure position of a printer for making extra prints from the film. If the notch is formed in the film at a location where a frame number bar code is printed, it is hard to read the frame number bar code. Therefore, it is difficult to form notches in a film on which frame number bar codes are previously printed and automatically read during processing, without disrupting the bar codes.
In view of the above, a superior printing system would be one in which it was unnecessary to form notches in a film having frame number bar codes. However, film without notches cannot provide timing signals for reading the frame number bar codes; accordingly, in such a system the frame number bar codes themselves should be positively read. This requires printing frame number bar codes of a higher quality than is possible with conventional DX bar codes on the film.
To print the frame number bar codes with a high quality, not only should the printing head form an optical bar code pattern which is sharp and uniform in density, but also the film to be printed should be accurately positioned during printing the bar codes, to avoid double exposures. In an attempt at avoiding a double exposed bar code (which is often formed due to the reverse movement of film caused by the fluttering of a moving film, oscillations of a film upon the film stops or a play of gears having backrush included in a film transporting system), there has been proposed a side printing apparatus in cooperation with a control system comprising a rotary encoder for providing encoder pulse signals in two different phases in synchronism with the transportation of film, a direction discriminator for discriminating the direction in which a film is transported to provide a forward direction signal or a reverse direction signal, an up-down counter for starting to count up the reverse direction signals and count down the forward direction signals, and means for restraining a light emitting printing head until the up-down counter counts down to zero. Such a side printing apparatus is known from Japanese Unexam. Patent Publ. No. 59-96966 (1984).
Another type of side printing apparatus, known from, for example, Japanese Unexam. Patent Publ. No. 63-106633 (1988), comprises an up-down counter for counting up forward direction pulse signals from a direction discriminator and counting down reverse direction pulse signals from the same. A carry signal of the up-down counter is used as a print timing signal. In such a side printing apparatus, the up-down counter counts down reverse direction pulse signals after the reverse of direction of transportation of a film, so that the amount of movement in the reverse direction can be effectively corrected.
Because forward direction pulse signals and reverse direction pulse signals are counted up and down in the above-noted side printing apparatus, it is essential that the forward and reverse direction signals do not overlap one another. However, in the case of generating the forward and reverse direction pulse signals from the encoder pulse signals of different phase, if the film violently oscillates in its moving direction, a reverse direction pulse signal or a forward direction pulse signal is often generated immediately after a forward direction pulse signal or a reverse direction pulse signal, respectively, depending upon the amplitude and cycle of oscillation of the film. Because, in such a case, a reverse direction pulse signal or a forward direction pulse signal rises before the respective forward direction pulse signal or reverse direction pulse signal has fallen, the up-down counter makes an error and does not count either one of the forward or the reverse direction pulse signal. That is, because of the direction discriminator consisting of an integral logic circuit for determining whether an encoder pulse signal is at a high level (H) or a low level (L) with an associated threshold level, if the film oscillates at the transition of an encoder pulse signal between the high level (H) and the low level (L), then the rotary encoder repeatedly turns in both directions, so as to provide incomplete encoder pulse signals. Accordingly, the conventional direction discriminators have difficulty in positively following the changes of film movement direction so as to make the measurement of film transportation with a high degree of accuracy. This results in a difficulty in completely preventing a double exposure, whereby it would be possible to print a sharp bar code pattern on a film, which is automatically readable by means of a bar code reader.
If the rotary encoder, which is rotated by the film to detect the length of movement of the film, encounters operational failures or errors causing the interruption of encoder pulse signals, it is impossible to continue the measurement of film transportation. That is, if signals from the rotary encoder are interrupted due to breakdowns of the rotary encoder itself or elements of the signal transfer line, poor contacts of connectors, a mechanical failure in attaching the rotary encoder including loosened coupling, or a mechanical stress accumulated in the rotary encoder, then it is judged that the film has stopped and accordingly, printing is interrupted. The bar code print pattern is thus destroyed. As a result, a single bar of a bar code will be separated into two thin bars if the film stops such that a region where a bar code is to be printed is disposed in a printing position, or a wide space will be formed between two bars of a bar code if the film stops such that a region where a bar code is not to be printed is disposed in a printing position. In either case, such a bar code is incorrectly read by an automatic bar code reader.
Bar codes are generally printed with monocolor light. To provide the printing light, although it is possible to use the same color of light-emitting elements, it is preferred to use different colors of light and mix the different colors of light to provide monocolor light, with regard to the efficiency of coloration. For this reason, a plurality of light-emitting diodes or laser diodes having different wavelengths have heretobefore been used. Such light-emitting elements are driven by means of a drive circuit such as described in, for example, Japanese Unexam. Pat. Publ. No. 63-46409 (1988).
The drive circuit described in this publication is adapted to drive four LEDs having three different wavelengths, using six transistors to control an exposure. This drive circuit, although capable of providing a desired color of light, is complex in its structure for mixing different colors of light to form a monocolor of light. It is also difficult, controlling an exposure by controlling the times for which the LEDs emit light, to print bar codes on films having different film speeds. For example, because commercially available films have film speeds between 10 and 3200 ISO standard, and the fastest and slowest films thus differ in sensitivity by a factor of 320, if it is necessary to expose the fastest film for one (1).mu. second, then the slowest film should be exposed for approximately 320.mu. seconds. 320.mu. seconds necessary to print on a moving film is too long to be neglected. If it is difficult to print on a moving film for a short exposure time, there is caused a blur of print pattern. Such a blur of print pattern if significant, results in narrow printed bars or narrow spaces between printed bars.
To solve the above problem, it has been proposed to change a drive voltage for the light-emitting elements. However, if a suitable voltage is not selected, an edge effect is caused in the printed bar code due to overexposure, or a dull color of bar code is formed due to underexposure. In either case, it is difficult for the resulting bar code to be automatically read.